Like James we have standard 4ft high stock fencing, we have never had any escapees out of the field. We have British Toggenburgs, Anglo-nubians, British Alpines, and they are all breeds probably more likely to try and escape than golden guernsey's would be.
We also have 4ft high hurdles which we use to pen them at night etc, and apart from an over enthusiastic male billy kid who wanted to get to a girl goat in season, we haven't ever had any of them escape from them either.
Beth